arXiv subjects

P. G. Mercadante

Publications and source records attributed to P. G. Mercadante.

At least 19 recordsLinked to original sources

arXiv2025

Brazilian Report on Dark Matter 2024

One of the key scientific objectives for the next decade is to uncover the nature of dark matter (DM). We should continue prioritizing targets such as weakly-interacting massive particles (WIMPs), Axions, and other low-mass dark matter candidates to improve our chances of achieving it. A varied and ongoing portfolio of experiments spanning different scales and detection methods is essential to maximize our chances of discovering its composition. This report paper provides an updated overview of the Brazilian community's activities in dark matter and dark sector physics over the past years with a view for the future. It underscores the ongoing need for financial support for Brazilian groups actively engaged in experimental research to sustain the Brazilian involvement in the global search for dark matter particles

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arXiv2019

Brazilian Community Report on Dark Matter

This white paper summarizes the activities of the Brazilian community concerning dark matter physics and highlights the importance of financial support to Brazilian groups that are deeply involved in experimental endeavours. The flagships of the Brazilian dark matter program are the Cherenkov Telescope Array, DARKSIDE, SBN and LHC experiments, but we emphasize that smaller experiments such as DAMIC and CONNIE constitute important probes to dark sectors as well and should receive special attention. Small experimental projects showing the potential to probe new regions of parameter space of dark matter models are encouraged. On the theoretical and phenomenological side, some groups are devoted to astrophysical aspects such as the dark matter density profile while others explore the signature of dark matter models at colliders, direct and indirect detection experiments. In summary, the Brazilian dark matter community that was born not long ago has grown tremendously in the past years and now plays an important role in the hunt for a dark matter particle.

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arXiv2019

Advancing LHC Probes of Dark Matter from the Inert 2-Higgs Doublet Model with the Mono-jet Signal

The inert 2-Higgs Doublet Model (i2HDM) is a well-motivated minimal consistent Dark Matter (DM) model, but it is rather challenging to test at the Large Hadron Collider (LHC) in the parameter space allowed by relic density and DM direct detection constraints. This is especially true when considering the latest XENON 1T data on direct DM searches which we use here to present the best current combined limit on the i2HDM parameter space. In this analysis, we present prospects to advance the exploitation of DM mono-jet signatures from the i2HDM at the LHC, by emphasising that a shape analysis of the missing transverse momentum distribution allows one to sizably improve the LHC discovery potential. As a key element of our analysis, we explore the validity of using an effective vertex, $ggH$, for the coupling of the Higgs boson to gluons using a full one-loop computation. We have found sizeable differences between the two approaches, especially in the high missing transverse momentum region, and incorporated the respective K-factors to obtain the correct kinematical distributions. As a result, we delineate a realistic search strategy and present the improved current and projected LHC sensitivity to the i2HDM parameter space.

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arXiv2008

Heavy-flavour tagging and the supersymmetry reach of the CERN Large Hadron Collider

The branching fraction for the decays of gluinos to third generation quarks is expected to be enhanced in classes of supersymmetric models where either third generation squarks are lighter than other squarks, or in mixed-higgsino dark matter models constructed to be in concordance with the measured density of cold dark matter. In such scenarios, gluino production events at the CERN Large Hadron Collider should be rich in top and bottom quark jets. Requiring b-jets in addition to missing transverse energy should, therefore, enhance the supersymmetry signal relative to Standard Model backgrounds from V + jet, VV and QCD backgrounds (V=W, Z). We quantify the increase in the supersymmetry reach of the LHC from b-tagging in a variety of well-motivated models of supersymmetry. We also explore ``top-tagging'' at the LHC. We find that while the efficiency for this turns out to be too low to give an increase in reach beyond that obtained via b-tagging, top-tagging can indeed provide a confirmatory signal if gluinos are not too heavy. Finally, we explore the prospects for detecting the direct production of third generation squarks in models with an inverted squark mass hierarchy. This is signalled by b-jets + missing transverse energy events harder than in the Standard Model, but softer than those from the production of gluinos and heavier squarks. We find that while these events can be readily separated from SM background (for third generation squark masses ~300-500 GeV), the contamination from the much heavier gluinos and squarks remains formidable if these are also accessible.

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arXiv2005

Using b-tagging to enhance the SUSY reach of the CERN Large Hadron Collider

Assuming that supersymmetry is realized with parameters in the hyperbolic branch/focus point (HB/FP) region of the minimal supergravity (mSUGRA) model, we show that by searching for multijet + missing E_T events with tagged b jets the reach of experiments at the LHC may be extended by as much as 20% from current projections. The reason for this is that gluino decays to third generation quarks are enhanced because the lightest neutralino has substantial higgsino components. Although we were motivated to perform this analysis because the HB/FP region is compatible with the recent determination of the relic density of cold dark matter, our considerations may well have a wider applicability since decays of gluinos to third generation quarks are favoured in a wide variety of models.

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arXiv2004

Neutrinos in Anomaly Mediated Supersymmetry Breaking with R-Parity Violation

We show that a supersymmetric standard model exhibiting anomaly mediated supersymmetry breaking can generate naturally the observed neutrino mass spectrum as well mixings when we include bilinear R-parity violation interactions. In this model, one of the neutrinos gets its mass due to the tree level mixing with the neutralinos induced by the R-parity violating interactions while the other two neutrinos acquire their masses due to radiative corrections. One interesting feature of this scenario is that the lightest supersymmetric particle is unstable and its decay can be observed at high energy colliders, providing a falsifiable test of the model.

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arXiv2001

Anomaly Mediated Supersymmetry Breaking without R-Parity

We analyze the low energy features of a supersymmetric standard model where the anomaly--induced contributions to the soft parameters are dominant in a scenario with bilinear $R$--parity violation. This class of models leads to mixings between the standard model particles and supersymmetric ones which change the low energy phenomenology and searches for supersymmetry. In addition, $R$--parity violation interactions give rise to small neutrino masses which we show to be consistent with the present observations.

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arXiv2001

Direct Signals for Large Extra Dimensions in the Production of Fermion Pairs at Linear Colliders

We analyze the potentiality of the new generation of $e^+e^-$ linear colliders to search for large extra dimensions via the production of fermion pairs in association with Kaluza-Klein gravitons (G), i.e. $e^+e^- \leftarrow f\bar{f}G$. This process leads to a final state exhibiting a significant amount of missing energy in addition to acoplanar lepton or jet pairs. We study in detail this reaction using full tree level contibutions due to the graviton emission and the standard model backgrounds. After choosing the cuts to enhance the signal, we show that a linear collider with a center-of-mass energy of 500 GeV will be able to probe quantum gravity scales from 0.96(0.86) up to 4.1(3.3) TeV at 2(5)$σ$ level, depending on the number of extra dimensions.

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arXiv2000

Low-Scale and Gauge-Mediated Supersymmetry Breaking at the Fermilab Tevatron Run II

The prospects for discovering and studying signals of low-scale supersymmetry breaking models at the Tevatron Run II and beyond are explored. These models include gauge-mediated supersymmetry breaking as the most compelling and concrete realization, but more generally are distinguished by the presence of a nearly massless Goldstino as the lightest supersymmetric particle. The next-lightest supersymmetric particle(s) (NLSP) decays to its partner and the Goldstino. Depending on the supersymmetry breaking scale, these decays can occur promptly or on a scale comparable to or larger than the size of a detector. A systematic analysis based on a classification in terms of the identity of the NLSP and its decay length is presented. The various scenarios are discussed in terms of signatures and possible event selection criteria. The Run II and beyond discovery and exclusion reaches, including the effects of background, are detailed for the most compelling cases. In addition to standard event selection criteria based on missing energy and photons, leptons, jets, taus, tagged b-jets, or reconstructed Z-bosons, more exotic signals of metastable NLSPs such as displaced photons, large negative impact parameter tracks, kink tracks, both opposite and same-sign highly ionizing tracks, time of flight measurements, charge-changing tracks, charge-exchange tracks, and same-sign di-top events are investigated. The interesting possibility of observing a Higgs boson signal in events that are efficiently "tagged" by the unique signatures of low-scale supersymmetry breaking is also considered.

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arXiv1999

Analyses of Long Lived Slepton NLSP in GMSB Model at Linear Collider

We performed an analysis on the detection of a long lived stau at a linear collider with $\sqrt{s}=500$ GeV. In GMSB models a long lived NLSP is predicted for large value of the supersymmetry breaking scale F. Furthermore in a large portion of the parameter space this particle is a stau. Such heavy charged particles will leave a track in the tracking volume and hit the muon detector. In order to disentangle this signal from the muon background we explore kinematics and particle identification tools: time of flight device, dE/dX and Cerenkov devices.

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arXiv1999

Diphoton Signals for Large Extra Dimensions at the Tevatron and CERN LHC

We analyze the potentiality of hadron colliders to search for large extra dimensions via the production of photon pairs. The virtual exchange of Kaluza--Klein gravitons can significantly enhance this processes provided the quantum gravity scale ($M_S$) is in the TeV range. We studied in detail the subprocesses $q \bar{q} \to γγ$ and $g g \to γγ$ taking into account the complete Standard Model and graviton contributions as well as the unitarity constraints. We show that the Tevatron Run II will be able to probe $M_S$ up to 1.5--1.9 TeV at 2$σ$ level, while the LHC can extend this search to 5.3--6.7 TeV, depending on the number of extra dimensions.

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arXiv1999

The Reach of Tevatron Upgrades in Gauge-Mediated Supersymmetry Breaking Models

We examine signals for sparticle production at the Tevatron within the framework of gauge mediated supersymmetry breaking models for four different model lines, each of which leads to qualitatively different signatures. We identify cuts to enhance the signal above Standard Model backgrounds, and use ISAJET to evaluate the SUSY reach of experiments at the Fermilab Main Injector and at the proposed TeV33. For the model lines that we have examined, we find that the reach is at least as large, and frequently larger, than in the mSUGRA framework. For two of these model lines, we find that the ability to identify $b$-quarks and $τ$-leptons with high efficiency and purity is essential for the detection of the signal.

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arXiv1998

Searching for Bottom Squarks at Luminosity Upgrades of the Fermilab Tevatron

Because of their Yukawa interactions, third generation squarks may be substantially lighter than those of the first two generations. Assuming that $\tb_1 \to b\tz_1$ and $\tz_1$ escapes experimental detection, we show that experiments at the Main Injector upgrade (integrated luminosity of $2 fb^{-1}$) of the Tevatron should be sensitive to $b$-squark masses up to 210 GeV for $m_{\tz_1} \leq 120$ GeV. For integrated luminosities of $10 fb^{-1}$ (25 $fb^{-1}$) the sbottom mass reach increases by 20 GeV (35 GeV). If the channel $\tb_1 \to b\tz_2$ is also accessible, the reach becomes model-dependent and may be degraded relative to the case where only the decay to $\tz_1$ is allowed. In models with gaugino mass unification and $μ$ much larger than gaugino masses, we argue that this degradation is unlikely to be larger than 30-40 GeV.

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arXiv1998

Signal and Backgrounds for the Single Production of Scalar and Vector Leptoquarks at the LHC

We perform a detailed analysis of the potentiality of the CERN Large Hadron Collider to study the single production of leptoquarks via $pp \to e^\pm q\to$ leptoquark $\to e^\pm q$, with $e^\pm$ generated by the splitting of photons radiated by the protons. Working with the most general $SU(2)_L \otimes U(1)_Y$ invariant effective lagrangian for scalar and vector leptoquarks, we analyze in detail the leptoquark signals and backgrounds that lead to a final state containing an $e^\pm$ and a hard jet with approximately balanced transverse momenta. Our results indicate that the LHC will be able to discover leptoquarks with masses up to 2--3 TeV, depending on their type, for Yukawa couplings of the order of the electromagnetic one.

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arXiv1995

Top pair production with an extra gluon at the Tevatron

We calculate top pair production and decay at the Tevatron $p\bar p$ collider, with the emission of an extra gluon, and study the corresponding $W+5$\,jet top signals including full spin correlations in the $W \to \ellν$ leptonic and $W\to jj$ hadronic decays. We study the feasibility of reconstructing $W+5$\,jet top events with a single $b$-tag, including realistic energy resolution. Our suggested basic procedure based on kinematic fitting achieves about 74\% reconstruction efficiency, with 74\% of the reconstructed events correctly classified (purity); this improves to 82\% efficiency with 77\% purity in double-$b$-tagged events. We suggest possible refinements, based on virtuality criteria, that give higher purity at the cost of lower reconstruction efficiency.

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arXiv1995

Anomalous g^5_z coupling at $γγ$ colliders

We study the constraints on the anomalous coupling $g^Z_5$ that can be obtained from the analysis of the reaction $γγ\rightarrow W^+ W^- Z$ at future linear $e^+e^-$ colliders. We find out that a $0.5$ ($1$) TeV $e^+e^-$ collider operating in the $γγ$ mode can probe values of $g_5^Z$ of the order of $0.15$ ($4.5 \times 10^{-2}$) for an integrated luminosity of $10$ fb$^{-1}$. This shows that the ability to search for this anomalous interaction of the $γγ$ mode is better than the one of the usual $e^+e^-$ mode, and it is similar to the ability of the $eγ$ mode.

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arXiv1995

Quartic Anomalous Couplings in $γγ$ Colliders

We study the constraints on the vertices $W^+W^- Zγ$, $W^+W^-γγ$, and $ZZγγ$ that can be obtained from triple-gauge-boson production at the next generation of linear $e^+e^-$ colliders operating in the $γγ$ mode. We analyze the processes $γγ\to W^+W^-V$ ($V=Z$, or $γ$) and show that these reactions increase the potential of $e^+e^-$ machines to search for anomalous four-gauge-boson interactions.

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arXiv1993

Triple Vector Boson Processes in $γγ$ Colliders

We study the production of three gauge bosons at the next generation of linear $e^+e^-$ colliders operating in the $γγ$ mode. The processes $γγ\rightarrow W^+W^-V$ ($V=Z^0$, or $γ$) can provide direct information about the quartic gauge-boson couplings. We analyze the total cross section as well as several dynamical distributions of the final state particles including the effect of kinematical cuts. We find out that a linear $e^+e^-$ machine operating in the $γγ$ mode will produce 5--10 times more three-gauge-boson states compared to the standard $e^+e^-$ mode at high energies.

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